Why "GetMailingOpens" method from Responses retuns 0 "Fields" dictionary collection for all opened recipients given mailingID?

[MilSix]

Hello Kyle,
When I call GetMailingOpens method given MailingID to retrieve opened mail recipients to save mailed sent status to individual records to our system. I've notice that the method "GetMailOpens" only returned list of opened mail members and did not return "Fields" collections. Collection for each opened member with Fields count is 0. for both key and value set... Is it an api bug?
The sample Response output for this method shows fields information in inner array.
We have up to 30 users defined fields in "Fields" collection, and hope we can get at least 3 keys information back in order to verify member in our system since we have shared email address scenarios. Please advise.

[MilSix]